There has been a large change in shopping habits over the last 20 years.
When QVC started, I found one of the best things about it was that you saw a product, and if it was on air, it was IN STOCK. No disappointment of trailing round town, only to find they haven't got the size/colour you want. Added to that the 30-day mbg and it was attractive. Carrying large stock is expensive and doesn't 'look good' on the balance sheet and most large sellers don't carry volumes, e.g. electrical appliance retailers, DIY, furniture and the increase in internet shopping has boosted many of these companies. Amazon, starting as a bookseller, now fronts multiple companies as a shop window and has invested in its website and delivery methods. I'm pretty sure Q is trying to reduce its stock volumes, hence waitlists and advanced orders and, to me, that is a turn-off as I can usually get these brands elsewhere, quicker and cheaper. Add to that the fact that many brands which were once hard to get other than on Q, are now widely available.
I don't think they are likely to disappear any time soon but the future certainly looks more samey and much less interesting!